During ophthalmic examination visual processing speed is not taken into account. However, there are children who experience problems in daily life, which appear to be caused by slowed visual perception. At present, there are no clinical tests which allow testing of visual acuity and processing speed simultaneously. Our aim was to develop such a test to quantify delays in visual processing and to collect normative data for children between 5 and 12 years. Additionally, we applied the test in children with visual impairments (VI) to assess their visual processing speed. 104 children with normal vision (9.4±2.0 years) and 52 children with VI (8.4±1.8 years) performed the speed-acuity test. The test consisted of 2x90 trials and they had to indicate as fast and accurate as possible on which side the opening of a Landolt-C was located using button presses. Nine sizes of the Landolt-C were used, sizes ranged from below visual acuity threshold to at least 0.6 LogMAR above visual acuity threshold. The drift-diffusion model was used to analyse the results. This decision-making model assumes that the brain accumulates (noisy) sensory evidence over time until the 'evidence scores' reach a decision boundary. The normative data revealed that the acuity thresholds obtained with the new test are comparable to those obtained with the Freiburg visual acuity test. Additionally, the results showed that optotype-size has a significant influence on the reaction time. The reaction times decrease as optotype-size increases until they reach a minimum. The drift-diffusion model can account for these results. Furthermore, as children grow older they become faster. A substantial number of children with VI had slower visual processing compared to the normative data. In conclusion, the speed-acuity test is an effective tool to determine impairments in visual acuity and processing speed in clinical populations.